Harvesting root crops, such as beets, turnips and carrots, and tuber crops, such as potatoes and sweet potatoes, presents unique problems because the roots and tubers develop well below the surface of the soil. Potatoes, for example, typically grow up to 12 inches below the surface. Thus, in order to harvest these crops, the roots or tubers must be lifted from the soil and separated from considerable quantities of soil, clods, rocks, stems, and other debris. In addition, as most root and tuber crops have a very high water content and little, if any, protective covering, they can be easily damaged by impact with other objects. Thus, vertical drops within the harvester must be minimized.
Typical potato, or tuber, harvesters utilized in the United States, such as those currently manufactured by the Grimme Group (headquarted in Damme, Germany), and those previously manufactured by Lockwood Corporation (of Gering, Nebr.); Logan Corporation (of Logan, Iowa), Double L Manufacturing (of American Falls, Id.), and Thomas Equipment (of Centerville, New Brunswick, Canada), are typically equipped with a front blade that breaks up the soil and dislodges the tubers as it is pulled through the ground. Continual forward movement of the blade also forces the dislodged tubers, along with their stems, and a considerable amount of soil, clods, rocks and other debris onto a recirculating conveyor surface that transports the tubers, soil, clods, rocks and debris toward the rear of the harvester. The conveyor surfaces typically consist of parallel bars that are aligned perpendicular to the direction of travel, spaced about 50 mm (about 2 inches) apart, and interconnected by heavy belting. Historically, the conveyer surfaces were formed from steel rods that had interlinked loops at their ends and midpoint so as to form a broad chain that looked like a moving grate made of parallel bars. Though the looped interlinkages have generally been replaced by the heavy belting, which is much less susceptible to the abrasive action of silica sand particles in the soil, the conveyors are still referred to as elevator, harvester, or digger “chain.” Specifically, when the rods are affixed to heavy belting, this conveyor surface is called “belted chain.” Two belted chains are typically used on each potato harvester. The first, or primary, belted chain moves the potatoes mostly rearward, but also slightly upward. The conveyor drive and support sprockets associated with the primary belted chain are designed to shake the conveying surface, thereby causing loose soil, rocks, and debris to fall through the parallel rods of the belted chain as the harvested potatoes are moved rearward on the harvester. The second, or secondary, belted chain functions mainly to elevate the potatoes and subsequently drop them and the remaining soil, rocks and debris onto a transverse conveyor positioned at the upper rear of the potato harvester. The transverse conveyor may be constructed either of parallel rods or of powered finger rollers. Then potatoes are then deposited on a slanted elevator conveyor, which moves them upward, toward the front of the harvester, and loads them onto a “cleaning table.” Such a cleaning table is disclosed in U.S. Pat. No. 4,471,876 to John Stevenson, Jr., et al. The cleaning table sorts newly harvested tubers or root crops of at least a set minimum size from vines, soil, clods, rocks, other debris, as well as from harvested tubers or root crops that are smaller than the set minimum size. The table includes an inclined deck comprised of a plurality of spaced apart, parallel longitudinal rollers that operate in pairs, rotating toward one another when viewed from the top. The rollers are formed of a resilient, deformable material such as rubber, soft plastic or the like. One of each pair of rollers can have an elongate helical rib, flute, or flight extending from end to end. As the tubers or root crops and associated debris roll longitudinally down the table over the rollers, vines, soil, clods, stones, other debris, and small tubers or root crops are pulled into the gaps between the counter-rotating pairs of rollers and fall to the ground. Hard objects pass through the resilient, deformable rollers without causing damage to the rollers. Cleaning tables having rollers arranged with their rotational axes in a generally level plane, which rotate in the same direction, have also been designed and manufactured. This type of level cleaning table typically uses multiple star rollers, each of which has a series of resilient, evenly-spaced, star-shaped flanges positioned along its length. The rotating star rollers cause the crop load to advance from one side of the cleaning table to the other. Objects in the load, which are smaller than a fixed size are pulled through the table by the resilient projections on the star-shaped flanges of the rollers and fall to the ground. The pitch between rollers on most cleaning tables is adjustable, so that the size and amount of material discarded can be varied.
After passing the cleaning table, the tuber or root crop load falls onto a boom conveyor made of belted chain, which drops finally drops the potatoes into a self-unloading bulk truck, which drives in unison with the harvester. The technology used in potato harvesters to separate the potatoes from the soil, clods, rocks and debris is old and has changed very little since the introduction of early patented potato harvesters. U.S. Pat. No. 1,650,753 to Charlie Jasperson and U.S. Pat. No. 1,715,218 to Frank R. Wright, et al. are representative examples of such early potato harvesters. On each of these harvesters, a slanted conveyor of parallel rods moves the potatoes upward while letting the soil and debris fall through to the ground. Inasmuch as soil cushions the potatoes from injury, called “bruising,” the removal of soil from the potatoes too early during the harvesting process increases bruising. Thus, harvester operating speed is optimally adjusted so that the soil is removed from the potatoes and falls between the conveyor rods to the ground just before the potatoes are deposited into the accompanying truck. Padded, or flighted, conveyor rods are used to cushion the potatoes at drop points and prevent rollback on the elevator sections.
A significant advance in soil removal methodology was provided by a stone separation table that is the subject of U.S. Pat. No. 5,425,459 to Malcolm P. Ellis, et al. The stone separation table can be incorporated into a standard harvester for potatoes or other root crops at one of the horizontal conveying levels, and is typically installed in the potato processing path just before the potatoes reach the loading boom. The stone separation table selectively separates and drops stones, clods, and soil between a series of coplanar rollers while conveying the potatoes or other root crops from one side of the table to the other. The table incorporates sets of rollers including separating and spacing rollers of substantially the same diameter. Unlike the rollers of some cleaning tables, all rollers are driven in the same direction of rotation. The separating rollers are constructed with projecting elements, which may be either projecting fingers of a star roller or bristles of a brush roller. Stones, clods, soil, other debris, and even small tubers are carried downward by the projecting elements of the separating rollers through the gaps between the separating rollers and their associated spacing rollers and allowed to fall to the ground. The distance between the separating rollers and the associated spacing rollers can be adjusted to change the size of stones, clods and small tubers that are dropped out. Typically, the separating table is set up to run with less than 2.5 cm (approximately 1 inch) gaps.
In addition to its use as a cleaning apparatus, the separating table can also be used as a sorter or sizer. When used as a sorter or sizer, the roller pitch is adjusted so that tubers smaller than a desired size drop through the table.
Problems Associated With Current Technology
Efficient soil and clod removal is the most difficult function for modern harvesting equipment. Soil that is not removed from the tubers will be transported to bulk storage facilities. Such residual soil greatly increases the likelihood of spoilage during storage. Thus, before tubers enter bulk storage, they are subjected to one or more cleaning steps, which may utilize chain conveyors, large cleaning tables, and even manual labor for hand removal of residual soil, clods, stones, and other debris. Soil removed during the final cleaning steps must be hauled back to the field.
Unfortunately, field conditions are highly variable. A harvester that functions properly in one portion of the field may pick up too much soil or clods in another. Tractor ground speed and power take off speeds are presently the only means for adjusting cleaning effectiveness of the harvester as it collects tubers from the field. Using currently-available technology, control over the size of tubers collected by a harvester is limited to selection of a desired spacing between the parallel rods of the belted digger chains and/or adjustment of the pitch—and, thus, gaps—between rollers which make up the separation table. For russet potatoes, which comprise about 80 percent of total US production, belted conveyor chains having a 50 mm center-to-center spacing of parallel rods are typically employed. As the rods are about 12.5 mm, or one-half inch, in diameter, the gaps between the rods are about 37.5 mm, or 1½ inch. Thus, tubers having a diameter of less than about 1½ inches will fall through the chain and be discarded. As belted digger chain is very expensive, the purchase of multiple sets of various sizes is usually not an option. In addition, the use of belted chain having more-closely-spaced rods for the recovery of smaller potatoes results in a much slower removal of soil, clods, stones, and other debris. As a result, harvester ground speed would need to be significantly reduced to allow sufficient cleaning to occur. Using currently-available technology, the economic loss caused by a reduction in harvester speed will not be offset by the extra value of smaller potatoes recovered using belted chain with narrower rod spacing.
On the other hand, even if harvester speed is reduced, tubers smaller than the gaps between the rods of the belted chain will fall through and be lost. Using currently-available technology, which sorts only by size, clods which are the same size or larger than the minimum size of tuber sought to be recovered cannot be automatically separated from the tubers. The present generation of tuber harvesters relies almost exclusively on vibration to break up clods. Consequently, even if harvester ground speed is reduced, the use of belted chain having more closely-spaced rods increases the soil cushioning, increases the load on the harvester, and hampers the disintegration of clods, causing more clods to be carried to storage. Thus, using available equipment, harvesting costs increase, and long-term storage of tubers suffers as the targeted size of harvested tubers decreases. Conversely, harvesting costs decrease and long-term storage of tubers improves as the targeted size of harvested tubers increases. What tuber farmers attempt to do is determine an optimum size for recovered tubers that will result in the largest bottom line figure, which will be calculated by deducting harvesting costs from the revenue received from the sale of harvested crops following storage.
Another cleaning device that has been used heretofore by the vegetable and fruit packing industry, and to a limited extent by the U.S. potato industry, is known as a pintle belt conveyor. The traditional rods of a cleaning conveyor are replaced with closely spaced bars to which are attached narrow, upright, soft coated fingers called “pintles”. The pintle belt conveyor has proven particularly adept at removing vines and grasses from the recovered crop. For this application, the pintle belt is placed on a steep incline, and the conveying surface of the pintle belt is run uphill. The harvested crop (e.g., tubers) is introduced at the top of the incline. As the individual vegetables, pieces of fruit, or tubers roll down the belt to a bottom conveyor, grasses and vines are caught by the fingers of the pintle belt. As the belt returns to the bottom of the incline, the grasses and vines are removed from the fingers, often with the aid of high-pressure air flows. The fruit, vegetables or tubers, clods and stones all roll to the bottom of the pintle belt, where they are collected by another conveyor belt. To date, the pintle belt has been used primarily to remove vines and grasses from the collected crop.
One manufacturer, Grimme Group, has used a generally level pintle belt conveyor coupled with a diagonally-positioned, powered roller—acting as an unloader, or shear—on a small, one-row tuber harvester. The roller, which is positioned so that its rotational axis is parallel to the upper surface of the pintle bent, spins in a direction opposite that of the surface of the pintle belt. In this application, the pintle belt conveyer and shear roller are positioned after the secondary set of chains, on the transverse conveyor. In the Grimme application, the entire load coming off of the secondary cleaning chains—including potatoes of all sizes, remaining stones, clods and other debris—is loaded onto and transported by the pintle belt conveyor. Vines and grasses are captured by the fingers of the pintle belt and pass beneath the spinning roller, while the potatoes, stones, and clods are offloaded by the spinning roller. In this application, the fingers of the pintle belt conveyor eliminates vines and grasses more effectively than a simple rod conveyor. Although the Grimme Group system eliminates vines and grasses better than a simple rod conveyor system, cleaning is not very effective, as the pintle belt and roller must deal with the entire harvested conveyor load, which includes potatoes of all sizes, as well as stones and clods. A spinning roller has also been commonly used on fixed location conveyor applications in potato packing plants to move potatoes from one conveyor to another.